Windows 7 Pro x 64 repair

One of our employees ended up with a corrupted anti-virus program and hence had tons of spyware / viruses.

I was able to repair it to an almost working state. On the last boot up, something went wrong. I must have accidentally deleted the wrong registry key.

The computer won't boot into save mode either.

I tried a system repair, but no luck. I thought I could do an upgrade, but the system says upgrades can only be performed from within the operating system.

The data on the hard drive is still good and I would like to access it.

Does anyone have any suggestions?

I suppose I could always install a fresh version of Windows (without erasing the hard disk), but my preference would be a repair of some sort. There are no previous restore points (the user disabled them).

The computer is a HP Folio 13 with SSD drive and Windows 7 Professional x64.

Take the drive out of the existing computer and add it as a secondary drive on another computer. Scan it for virus, malware and spyware first; then copy the desired data off the suspect drive. Once the data has been backed up, delete it's partition, re-create and reformat before returning it to the original computer, then reinstall the OS.

REGISTRY HIVES are the five files which stores the system registry and their file names are DEFAULT, SAM, SYSTEM, SECURITY and SOFTWARE and they are a set of system files which keeps the system running properly.

Since the days in fixing XP problems, we are playing around to fix computers by restoring the damaged registry from the backup registry hives.

The current registry hives are in the location below.
C:\Windows\System32\config\

The backup registry hives are in the location below.
C:\Windows\System32\config\RegBack

for such a system - i would not loose more time over repairs
backup and do a fresh install is the only guaranteed good solution
***you'll loose more time with repairs, and never be sure it is ok
i would not even try a parallel install, like you said

To get rid of the viruses: You could try doing a persistant install of linux on a USB and use it totransfer out the data to another USB drive. After this I would install the ClamAV on the linux usb, update Clam, and scan the system for virus and such. I have had this work very well the in past. You could also try Hirens.

To repair the reg: boot into Hirens, boot into the PE, and use the Registry Editor PE to access and modify registry keys. You can also the SFC command line tool to repair any system files.